A Little Princess by Frances Hodges Burnett. The rest of the beginning goes like so:

Once on a dark winter's day, when the yellow fog hung so thick and heavy in the streets of London that the lamps were lighted and the shop windows blazed with gas as they do at night, an odd- looking little girl sat in a cab with her father and was driven rather slowly through the big thoroughfares.

She sat with her feet tucked under her, and leaned against her father, who held her in his arm, as she stared out of the window at the passing people with a queer old-fashioned thoughtfulness in her big eyes.

She was such a little girl that one did not expect to see such a look on her small face. It would have been an old look for a child of twelve, and Sara Crewe was only seven. The fact was, however, that she was always dreaming and thinking odd things and could not herself remember any time when she had not been thinking things about grown-up people and the world they belonged to. She felt as if she had lived a long, long time.

Cool. I bought a copy for the kids ages ago, but we haven't read that one yet.